Daniel et al. U.S. Pat. No. 3,908,385, issued Sep. 30, 1975 and entitled "Planted Surface Conditioning System", discloses a drainage system which utilizes vacuum to promote drainage of a natural turf athletic field. The system includes a water impermeable membrane over a compacted subsoil, covered by a fill layer of sand with a drainage network buried therein and a natural turf playing surface on top. Some of the pipes in the drainage network are fluid permeable, and vacuum may be applied to the network to assist gravity drainage during periods of heavy rainfall. Even without this feature of vacuum-enhanced drainage, the configuration of the subsurface components, and particularly the use of a horizontal water impermeable membrane, provides advantages in controlling the water level in the system.
Turf science and maintenance play significant roles in the performance of any vacuum-enhanced or water level controlled natural turf field. However, the relatively high initial cost of buying and installing the components of such a system are probably the most important factors considered when the decision to purchase such a system is made. Thus, while there exists a growing desire for such systems in the market, the systems must meet or exceed performance expectations when in use, and they must also be economically feasible at the outset. Due to ever-tightening budgets, even the most successful professional and university teams are extremely cost-conscious about their athletic facilities.
Partially in recognition of these economic realities, Mr. Daniel improved upon his original athletic field drainage system with vacuum-enhanced drainage capability. These improvements are set forth in U.S. Pat. No. 5,350,251, issued Sep. 27, 1994 and entitled "Planted Surface Moisture Control System". The system disclosed in Daniel '251 results in reduced installation and construction costs for a drainage system by eliminating the underground concrete vacuum pump pits used in earlier systems. Daniel '251 indicates that such underground concrete pump pits were relatively expensive, were required to meet stringent building requirements which varied from community to community, and sometimes required the removal of existing stadium sections.
Thus, one primary objective of the system of Daniel '251 related to reducing the cost of the vacuum-enhanced drainage feature for an athletic field drainage system. It is an object of this invention to follow this lead one step further, to further reduce the time and costs associated with installing and constructing a drainage system for an athletic field, with or without vacuum-enhanced drainage capability.
Many small colleges or high schools simply cannot afford to spend the relatively large amounts of money on athletic facilities that are spent by some professional teams or major universities. Nevertheless, for these entities, there still remains a strong desire to obtain the best facilities possible within the given financial constraints. This includes the desire to purchase and install natural turf athletic fields which have the advantages of consistent drainage, a level playing surface and the ability to exercise some degree of control over the moisture content of the natural turf and the fill layers residing therebeneath, regardless of whether or not the system also provides the feature of vacuum-enhanced drainage to accommodate periods of heavy rainfall. It is another object of the invention to meet the needs of these entities by improving the degree of control over the drainage or moisture content of a natural turf athletic field, regardless of whether or not achievement of this control includes the feature of vacuum-enhanced drainage.
Some entities may desire an athletic field with optimum capabilities, particularly vacuum-enhanced drainage, but this desire for these optimum capabilities may not become apparent until after a prior system has already been installed. In these instances, there is a need to supply improved features for an athletic field, such as vacuum-enhanced drainage, after the system has already been installed. Accordingly, it is still another object of the invention to facilitate the upgrading of an in-place drainage system for an athletic field, to add improvement features such as vacuum-enhanced drainage.
For a number of presently in-place systems which provide vacuum-enhanced drainage for an athletic field, the systems were originally designed to achieve vacuum-enhanced drainage in an automatic mode. Some systems were also designed to provide subirrigation or overhead irrigation in an automatic mode. Based on experience and knowledge in this field, applicants have concluded that these systems generally have not achieved a high degree of reliability in delivering this automatic mode of operation. In other words, applicants have concluded that automatic sensing of excess or insufficient moisture within the system, for the purpose of automatically initiating vacuum drainage or subirrigation (and/or overhead irrigation), respectively, has worked better in theory than in practice. Also, these so-called automatic systems have not satisfactorily integrated gravity drainage and vacuum-enhanced drainage.
Therefore, it is still another object of the invention to increase the reliability of athletic field drainage systems which include automatic control of features such as vacuum-enhanced drainage or irrigation cycles, and to do so in a manner which also integrates gravity flow drainage.
Applicants have also come to recognize that regardless of the degree of complexity and/or the number of features provided by a drainage system for an athletic field, consistent and uniform gravity drainage of excess water remains one of the most important features of an athletic field. To achieve consistency and uniformity in the gravity drainage of excess water from an athletic field, most fields incorporate a drainage pipe system buried beneath the turf. In installing such a drainage pipe system, grading the subsurface to a desired level within a predetermined tolerance and then locating the drainage network beneath the subsurface grade represents a substantial cost. Also, the labor costs associated with interconnecting the separate pieces of drainage pipe are relatively high, due to the time required to lay out and interconnect the separate piping pieces at different horizontal levels. These different horizontal levels also present the problem of determining the optimum level for placement of moisture sensors, for automatic mode of operation.
It is still another object of this invention to reduce the costs associated with constructing and installing a drainage network beneath a natural turf athletic field, and to simplify and remove the uncertainty associated with locating and installing moisture sensors used for automatic operation.
For some geographical areas it is difficult to maintain a healthy condition of the natural turf due to extended periods of cold weather, and eventual freezing of the ground. A number of prior systems for heating natural turf athletic fields have utilized electric cable heaters to either thaw the ground or keep it from getting frozen. Other systems for heating fields utilize heated air, steam or water, usually with the heating fluid remaining within a dedicated heat distribution and radiation network. Unfortunately, such systems typically require use of relatively high amounts of electrical energy. Moreover for those fields which use a separate subsystem for heating the field, the existence of two distinct subsystems tends to complicate installation, operation and/or maintenance of both subsystems.
It is still another objective of the invention to increase cost efficiency and energy efficiency in heating a natural turf field during periods of cold weather, and to do so in a manner which does not significantly increase the complexity or cost of installing, operating or maintaining the field system.